氨碱法蒸馏系统300 m3预灰桶搅拌桨流场数值模拟分析

氨气蒸馏是氨碱法生产纯碱的重要工序，其中预处理设备预灰桶的搅拌混合效果会直接影响蒸氨效率。因此，系统研究预灰桶内的流场分布，对纯碱工业的发展具有一定现实意义。基于流体力学对预灰桶内流体流动情况进行了计算，分析了工业常用吊链式搅拌桨预灰桶内流场分布。吊链式搅拌中流体以切向流为主，混合效果差。进一步对预灰桶搅拌桨叶进行了选型，分析了斜叶桨、六斜叶圆盘涡轮桨和六直叶圆盘涡轮桨3种桨型以及不同搅拌层数的流场分布，结果表明双层六斜叶圆盘涡轮桨混合效果最好。研究结果对氨碱法制碱工业中预灰桶搅拌设备的选型和设计提供了参考。     

Numerical Investigation of the Effect of Impeller Design Parameters on the Performance of a Multiphase Baffle‐Stirred Reactor

The turbulent gas‐liquid flow field in an industrial 100‐m³ stirred tank was calculated by using computational fluid dynamics based on the finite‐volume method. Turbulent effects were modeled with the shear stress transport model, and gas‐liquid bubbly flow was modeled with the Eulerian‐Eulerian approach using the Grace correlation for the drag force interphase momentum transfer. The relative motion between the rotating impeller and the stationary baffled tank was considered by using a multiple frames of reference algorithm. The effects of Rushton and pitched‐blade impeller design parameters such as blade geometry, location, and pumping direction on the mixing performance were investigated. It was found that a combination of Rushton turbines with up‐pumping pitched‐blade turbines provides the best mixing performance in terms of gas holdup and interfacial area density. The approach outlined in this work is useful for performance optimization of biotechnology reactors, as typically found in fermentation processes.     

INVESTIGATIONS INTO PUMPING CHARACTERISTICS OF AXIAL FLOW IMPELLERS IN AN INTERNAL LOOP REACTOR FOR ANIMAL CELL CULTURE

This investigation was intended to aid in the selection of impeller design and operating conditions, which would exhibit minimum turbulence in an internal loop reactor for axial flow velocities up to 18 cm/s.

For this purpose we measured power consumption, liquid flow velocity and mixing time with two marine propellers (pitch ratio tan alpha =1 and 0.57, respectively) and with flat-blade fan-type impellers (blade angles 10 to 90°).

The present results showed that at flow velocities between 7 and 14 cm/s a reduction in the pitch ratio (tan alpha) of the marine propeller from 1 to 0.57 increased the mechanical flow efficiency.

In addition, the fan-type impeller with a blade angle of 20° displayed flow characteristics comparable to the marine propellers; therefore, owing to its simple design, the fan-type impeller offers a practical substitute for the marine propellers.

In cell culture, draft-tubes used in impeller-driven reactors (internal loop reactors) offer two important features:

1. They simplify the design and scale-up process over that of open-blade impellers (flow patterns are more uniform);

2. They provide a mechanical support for bubblte-free membrane oxygenators;

Furthermore, on the assumption that loop reactors display lower bulk turbulence than open blade impellers for similar power consumption, this investigation was intended to aid in the selection of impeller design and operating conditions which would exhibit maximum pumping efficiency (with minimum mixing).

For this purpose, using a pH tracer method, we determined mechanical flow efficiency and dimensionless mixing time, which served as parameters for pumping efficiency to establish the following specific design characteristics:

1. Bulk mixing decreases relative to bulk flow with increasing bulk flow (mixing therefore conforms to the flow-in-pipe model) for two marine propellers (pitch tan alpha = 1 and 0.57) and for fan-type impellers (variable pitch) up to a blade angle of 30°;

2. Liquid velocity increases directly proportional to impeller speed up to 17 cm/s for (above) propellers, as well as fan-type impellers with blade angles of less than 30°;

3. The mechanical efficiency of axial flow (liquid velocity/power input) increases by decreasing the impeller pitch of marine impellers from tan alpha = 1 to tan alpha = 0.57, in the range of 7-14 cm/s;

4. A fan-type impeller (variable pitch) with a pitch angle of 20° displayed flow velocity and mechanical efficiency values, which lay between those of the (above) two marine propellers.

Fan-type impellers are considerably simpler in construction and are simpler to modify than marine propellers; for this reason this impeller type serves as a useful investigational tool. In addition we have found that at an impeller of 20° this type of impeller may be used to substitute marine propellers with a pitch ratio between 1 and 0.57.

We also suggest that square pitch marine propellers are not the most suitable for reactors in which mechanical efficiency of axial flow is critical, such as those for “shear sensitive” animal and plant cells.     

Modelling heat transfer for pitched-blade turbines operating in the laminar range of mixing

To model heat transfer on a vessel wall in the laminar range of mixing, a two-dimensional hydrodynamic model was proposed. The model consisted of a simultaneous solution of the Kirchhoff-Fourier energy equation and equations of motion. The model was used for pitched-blade turbines operating in the laminar range of mixing. Experimental studies confirmed that the two-dimensional model could be used for heat calculation in the tank.     

MODELLING OF NON-STANDARD MIXERS STIRRED WITH MULTIPLE IMPELLERS†

Little attention has so far been devoted to characterizing fluid-dynamic behaviour of multiple-impeller mixers which are often implicitly modelled as perfectly stirred tanks.

In the present paper a study is made of this type of equipment—stirred with four turbines; either six- or four-flat-blade disc turbines were used. Mean local concentration inside the mixers was measured and experimental pulse-response curves were compared with the theoretical curves corresponding to two one-parameter models (i.e., a cascade of ideal stages with backmixing and one-dimensional diffusion model) and to perfect mixing.

The results of both analyses show that both the one-parameter models considered represent the actual fluid-dynamic behaviour quite satisfactorily and the model of perfect mixing can be considered only as a first approach for macromixing modelling purposes.

Extensive investigation was then carried out in order to determine the dependence of the characteristic parameter of the stagewise model on operating conditions. Certain anomalies regarding situations where non-Newtonian fluids are used are also presented.     

An experimental analysis on mixing and stoking of monodisperse spheres on a grate

A better understanding of the mixing and stoking process is crucial for an optimization of the combustion process on grate firing systems. Thus experimental studies were carried out to analyse the response of a particle assembly on varying grate operational parameters. To reduce the number of variables which affect the system a generic grate design was chosen and a material of monodisperse spheres was selected. The grate system applied uses vertically moving parallel bars to induce mixing. Different patterns of bar motion were created by linking the bars in groups of uniform movement. A transparent polycarbonate side wall gives optical access to front layer of spheres. The mixing process was measured and quantified by image analysis of this visible layer. When applying a constant number of bar strokes it is found that the mixing performance is independent of the bar velocity. However, mixing performance increases nearly linearly with the stroke length. It turned out that specific “movement patterns” could be identified which show improved mixing behaviour. The results provided here may also be used for comparison with simulations of the particle mixing with the Discrete Element Method (DEM).     

实现余热电站负荷自动调整的简易方法

介绍了WOODWARD505装置与DCS系统相结合,在水泥窑余热发电过程中,对汽轮机进行串级恒压控制方式运行的简易方法以及改进实施的过程。串级恒压控制方式可使汽轮机的运行更加平稳,实现了余热电站负荷的自动调整,减轻了中控人员的劳动强度。     

固体人造板乳化蜡的研制

针对固体人造板乳化蜡的配方和调配工艺条件进行了筛选、考察,得到了最佳配方和工艺条件,经过放大试验也验证了实验室确定的固体人造板乳化蜡的最佳配方及工艺条件合理可靠,产品质量符合指标要求,可以进行批量生产。     

弹性棒对仿生学柔性反应器的流体混合强化

在柔性反应器底部放置竖直的弹性硅胶棒（弹性棒），通过弹性棒运动对周围流体产生扰动，强化流体混合。基于酸碱中和脱色法和图像分析方法，研究了柔性反应器的混合过程和混合时间；通过混合时间定量评估了弹性棒的强化效果；并分别研究了弹性棒的位置和高度及柔性反应器系统的最大挤压深度和频率对流体混合行为的影响。结果表明：弹性棒的放置能够使柔性反应器内隔离区结构改变，混合时间减少。弹性棒位置靠近挤压头一侧时，对流体混合强化最明显。在弹性棒高度低于柔性反应器内液面时，弹性棒高度增加，强化效果增加。超过液面之后，继续增加弹性棒高度，强化效果没有进一步增加。当弹性棒靠近挤压头、高度超过液面且最大挤压深度为2.5cm，与没有弹性棒时相比混合时间减少了57%。在其他实验条件不变的前提下，最大挤压深度增加，强化效果增加。     

MIXING ENHANCEMENT BY FREQUENCY-SELECTIVE CHAOTIC ADVECTION IN A 3-D TIME-PERIODIC STOKES FLOW

A new 3-D periodic Stokes flow has been imagined and realized experimentally. It consists of axial Poiseuille flow superimposed on the 2-D tangential motion between two confocal ellipses that glide circumferentially so that the geometry is invariant. Chaotic streak lines obtained experimentally are compared to numerical simulations of this time-periodic flow. We next turn our attention to the problem of determining how to move the boundaries in order to obtain the most efficient mixing. Using a numerical experiment to study the advection of a passive scalar, we show that for a given 3-D mixer geometry and flow rate there is an optimum modulation frequency of the boundary displacement protocol for which the mixing process is most efficient. Furthermore, it is shown that chaotic advection can be regarded as a frequency-selective amplifier. This behavior is similar to that of fluid instability where external perturbations are amplified for a certain frequency range. For values above or below this range, perturbations are damped and the system is stable.     

MIXING ENHANCEMENT BY FREQUENCY-SELECTIVE CHAOTIC ADVECTION IN A 3-D TIME-PERIODIC STOKES FLOW

A new 3-D periodic Stokes flow has been imagined and realized experimentally. It consists of axial Poiseuille flow superimposed on the 2-D tangential motion between two confocal ellipses that glide circumferentially so that the geometry is invariant. Chaotic streak lines obtained experimentally are compared to numerical simulations of this time-periodic flow. We next turn our attention to the problem of determining how to move the boundaries in order to obtain the most efficient mixing. Using a numerical experiment to study the advection of a passive scalar, we show that for a given 3-D mixer geometry and flow rate there is an optimum modulation frequency of the boundary displacement protocol for which the mixing process is most efficient. Furthermore, it is shown that chaotic advection can be regarded as a frequency-selective amplifier. This behavior is similar to that of fluid instability where external perturbations are amplified for a certain frequency range. For values above or below this range, perturbations are damped and the system is stable.     

Numeric Simulation-Based Analysis of the Mixing Process in Anaerobic Digesters of Biogas Plants

Stirring systems with two rotational three-bladed propellers were analyzed using computational fluid dynamics. The propellers are located at three heights and seven angles in a tank with 9 m radius. The fluid was characterized by non-Newtonian rheology and simulated by applying the k-ε turbulence model and the standard k-ω model. Reynolds numbers were estimated. High fluid speeds were obtained with the propellers located at a height of 2 m and oriented at 90° with respect to the tank radius. In the top regions of the tank, the fluid velocity was generally less intense and less affected by the angle setting. The configurations identified as good mixing systems showed power consumptions broadly distributed around 30 kW.     

Synthesis of the fluid machinery network in a circulating water system

Energy consumption of the fluid machinery network in a circulating water system takes up a large part of energy consumption in the process industry, so optimization on the network will enhance the economic and environmental performance of the industry. In this paper, a synthesis approach is proposed to obtain the optimal network structure. The effective height curves are used as tools to perform energy analysis, so that the potential placement of water turbines and auxiliary pumps can be determined with energy benefit. Then economic optimization is carried out, by the mathematical model with the total cost as the objective function, to identify the branches for water turbines and auxiliary pumps with economic benefit. In this way, the optimal fluid machinery network structure can be obtained. The results of case study indicate that the proposed synthesis approach to optimize the fluid machinery network will obtain more remarkable benefits on economy, compared to optimizing only the water turbine network or pump network. The results under different flowrates of circulating water reveal that using a water turbine to recover power or adding an auxiliary pump to save energy in branches are only suitable to the flowrate in a certain range.     

Optimization of Improvable Flows by combining BAT Analysis and process simulation

This paper proposes a methodology to improve the sustainability of industrial processes combining two tools: BAT Analysis and process simulation. Both tools are jointly applied to identify the IF of the analyzed process, so that the most appropriate candidate techniques from an inventory can be selected. The selected alternatives are tested in different scenarios that are evaluated using simulation, which would determine the configuration that best improves the sustainability of the process. The combination of both tools in an integrated methodology will help decision makers to select the most sustainable configuration for a given process. The methodology is validated in a case study: a hydrogen production plant. After analysing several scenarios where different candidate techniques are implemented, results show that the IF identified can be highly improved when the appropriate combination of BAT is applied.     

Three-dimensional vibrational mixing

When working with disperse solid matter systems, one uses the effect of vibration in numerous processes. Solid matter mixing with vibration has only occurred in very simple units up to now. By means of the 3D-vibrational mixer from the company Kuston, Kleve, the influence of vibration on bulk materials and new mixing techniques are demonstrated. The 3D-vibrational mixer is suitable for liquids and solids, does not require mixing tools that need to be cleaned, and does not carry out rotary motions which would hinder incoming lines. It is used for mixing small amounts, where the mixing tank can be used simultaneously as the transportation container, so that a transfer is unnecessary. With the aid of 4 linear motors, the vibrational amplitudes and the frequencies can be varied within wide boundaries in all three spatial directions. By analyzing the vibrational system by means of Lissajous figures, it can be demonstrated that the optimal mixing effect occurs in the case of small frequency differences between the three axes. For freeflowing bulk materials, the best possible mixing state, the uniform coincidence mixing, is achieved after 2 min.     

密炼机中胶料的混炼工艺与填充因数研究

对不同硬度的三元乙丙橡胶、丁腈橡胶、天然橡胶和氯丁橡胶胶料在密炼机中的混炼工艺与填充因数进行研究。结果表明:胶料的分散过程分为生胶塑炼、添粉/吃粉、分散后结团、形成团聚体、软化、配合剂分散和细分散、配合剂分布以及形成复合结构8个阶段;影响混炼填充因数的因素主要为胶料粘度和硬度;胶料的粘度和硬度越高,混炼填充因数越小;混炼工艺确定后,以胶料最佳分散为目标,可确定适合的混炼填充因数。     

Optimization analysis of dual-purpose systems

This paper aims to analyze dual-purpose systems focusing the total cost optimization; a superstructure is proposed to present cogeneration systems and desalination technologies alternatives for the synthesis process. The superstructure consists of excluding components, gas turbines or conventional steam generators with excluding alternatives of supplying fuel for each combustion system. Also, backpressure or condensing/extraction steam turbine for supplying process steam could be selected. Finally one desalination unit chosen between electrically-driven or steam-driven reverse osmosis, multi-effect and multistage flash should be included. The analysis herein performed is based on energy and mass conservation equations, as well as the technological limiting equation of equipment. The results for ten different commercial gas turbines revealed that electrically-driven reverse osmosis was always chosen together with both natural gas and gasified biomass gas turbines.     

两层桨搅拌釜内混合过程的新二维单元串联模型

在直径为 1 86mm的立式搅拌釜内 ,利用热电偶—温差法测量了两层组合桨搅拌釜内的液相混合时间 ,试验中采用的搅拌桨有直叶圆盘涡轮和斜叶涡轮 (上推式斜叶涡轮 PTU和下压式斜叶涡轮 PTD) ;根据激光多谱勒测速仪对流场的测量结果 ,提出了一种新的二维单元串联模型 ,用该模型对两层组合桨搅拌釜内的混合过程进行了模拟 ,发现模拟值和实验值吻合较好。     

精对苯二甲酸氧化反应器中气体停留时间分布

对苯二甲酸的工业生产多采用对二甲苯液相催化氧化方法,因此,氧化气体的混合特性就成为氧化反应器设计、放大的重要参数。文中针对工业中采用的涡轮桨和斜叶桨组合搅拌反应器型式,以氢气为示踪剂,采用阶跃激发响应技术测定了不同气量、搅拌转速下气体停留时间分布,同时开展了对二甲苯氧化试验,了解了气体混合对氧化中间产物含量影响。研究结果表明,只有当搅拌桨叶尖速度高于一个临界值,使气体接近全混的状态,才能实现单釜氧化目的产物的高收率。